free to play concept is proven, and not the you are free to play by yourself in your own server method.
WW2 Online has solid fights going when I just tried it, and its obviously a subpar game, but it has free play for lower ranks. People enjoy the game and they pay for it.
This is beating a dead horse though, I think if early war planes were free, we'd have much better numbers. I for one would probably be one of the veterans that just stick to early war though.